An image forming apparatus including a video controller and an engine control unit, each serving as a control unit, is conventionally known. The video controller and the engine control unit can communicate with each other. If the engine control unit detects a change in an operational state of the image forming apparatus, the engine control unit notifies the video controller of the detected state change. Then, if the video controller receives the notification informing the occurrence of a state change, the video controller acquires information indicating detailed contents of the change having occurred in the image forming apparatus and performs control to synchronize the video controller with the engine control unit based on the acquired information. For example, according to a method discussed in Japanese Patent Application Laid-Open No. 9-185294, an engine control unit transmits a state change notification signal informing a state change having occurred in the image forming apparatus to a video controller, and the video controller identifies a state change status in the image forming apparatus based on the notified information.
In a case where the engine control unit and the video controller can constantly communicate with each other using the method discussed in Japanese Patent Application Laid-Open No. 9-185294, it is feasible to realize a real-time sharing of a state change occurring in the image forming apparatus. However, a recent image forming apparatus is operable in a power saving mode in which the standby power consumption is 1 W or less. To reduce the entire standby power consumption in the power saving mode, the image forming apparatus prevents the engine control unit and the video controller from communicating with each other. Thus, synchronizing the engine control unit with the video controller is difficult in such a communication interrupted state. For example, it is assumed that the operational mode shifts to the power saving mode in a state where the status of a paper feeding cassette is detected. Then, the paper feeding cassette is removed from the image forming apparatus during the power saving mode and then the paper feeding cassette is attached again to the image forming apparatus. In such a case, if the image forming apparatus terminates operating in the power saving mode, it will be only determined that the status of the paper feeding cassette is present. In other words, there is an issue that a state change of the paper feeding cassette may not be detected if the paper feeding cassette has been attached to or detached from the image forming apparatus during the power saving mode.